#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <sys/epoll.h>

constexpr int MAX_EVENT_NUM = 1024;
constexpr int BUFFER_SIZE = 10;

// 将文件描述符设成非阻塞的
int setnonblocking(int fd) {
    int old_option = fcntl(fd, F_GETFL);
    int new_option = old_option | O_NONBLOCK;
    fcntl(fd, F_SETFL, new_option);
    return old_option;
}

// 将 fd 上的 EPOLLIN 之策到 epollfd 指示的内核事件表中，供下一轮处理
// 这个描述感觉有点不太理解
void addfd(int epollfd, int fd, bool enable_et) {
    epoll_event event;
    event.data.fd = fd;
    event.events = EPOLLIN;
    if (enable_et) {
        event.events |= EPOLLET;
    }
    epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event);
    setnonblocking(fd);
}

void lt(epoll_event *events, int number, int epollfd, int listenfd) {
    char buffer[BUFFER_SIZE];
    for (int i = 0; i < number; i++) {
        int sockfd = events[i].data.fd;
        if (sockfd == listenfd) {
            struct sockaddr_in client;
            socklen_t client_addrlen = sizeof(client);
            int connfd = accept(listenfd, (struct sockaddr*)&client, &client_addrlen);
            addfd(epollfd, connfd, false);
        } else if (events[i].events & EPOLLIN) {    // 只要 socket 缓存中还有数据未读出就会触发这部分代码
            printf("event trigger once\n");
            memset(buffer, '\0', BUFFER_SIZE);
            int ret = recv(sockfd, buffer, BUFFER_SIZE - 1, 0);
            if (ret <= 0) {
                close(sockfd);
                continue;
            }
            printf("get %d bytes of content: %s\n", ret, buffer);
        } else {
            printf("something's wrong.\n");
        }
    }
}

void et(epoll_event* events, int number, int epollfd, int listenfd) {
    char buffer[BUFFER_SIZE];
    for (int i = 0; i < number; i++) {
        int sockfd = events[i].data.fd;
        if (sockfd == listenfd) {
            struct sockaddr_in client;
            socklen_t client_addrlen = sizeof(client);
            int connfd = accept(listenfd, (struct sockaddr*)&client, &client_addrlen);
            addfd(epollfd, connfd, true);
        } else if (events[i].events & EPOLLIN) {
            printf("event trigger once\n");
            // 因为这个事件对应的这部分代码不会重复触发，所以要一次对出所有的 socket 缓存数据
            while (1) {
                memset(buffer, 0, BUFFER_SIZE);
                int ret = recv(sockfd, buffer, BUFFER_SIZE - 1, 0);
                if (ret < 0) {
                    if (errno == EAGAIN || errno == EWOULDBLOCK) {  // 对非阻塞 I/O ，满足该条件说明数据已读取完毕
                        printf("read later\n");
                        break;
                    }
                    close(sockfd);
                    break;
                } else if (ret == 0) {
                    close(sockfd);
                } else {
                    printf("get %d bytes of content: %s\n", ret, buffer);
                }
            }
        } else {
            printf("something's wrong.\n");
        }
    }
}

int main(int argc, char** argv) {
    if (argc <= 3) {
        printf("usage: %s ip_address port_number et_mode\n", basename(argv[0]));
        return 1;
    }
    const char* const ip = argv[1];
    int port = atoi(argv[2]);
    int et_mode = atoi(argv[3]);

    int ret = 0;
    struct sockaddr_in address;
    bzero(&address, sizeof(address));
    address.sin_family = AF_INET;
    address.sin_port = htons(port);
    inet_pton(AF_INET, ip, &address.sin_addr);
    int listenfd = socket(PF_INET, SOCK_STREAM, 0);
    ret = bind(listenfd, (struct sockaddr*)&address, sizeof(address));
    assert(listenfd >= 0);

    ret = listen(listenfd, 5);
    assert(ret != -1);

    epoll_event events[MAX_EVENT_NUM];
    int epollfd = epoll_create(5);
    assert(epollfd != -1);
    addfd(epollfd, listenfd, true);
    
    while (1) {
        int ret = epoll_wait(epollfd, events, MAX_EVENT_NUM, -1);
        if (ret < 0) {
            printf("epoll failure\n");
            break;
        }
        if (et_mode) {
            et(events, ret, epollfd, listenfd);
        } else {
            lt(events, ret, epollfd, listenfd);
        }
    }
    close(listenfd);
    return 0;
}